http://www.androidtapp.com/recent-chart-of-android-fragmentation/
Quite interesting!
I'm very keen to see what Android do with version 3 (Sponge Cake or whatever they will call it). I've heard they'll cut the OS down to run on all types of phone and then let manufacturers bolt on extra bits as they see fit. Then we as users can upgrade if we want without breaking the phone. So for example the HTC Sense UI would have to run on top of Android in such a way that if the core OS was upgraded the UI would either still work or disable back to a stock Android without any issues. I wonder how manufacturers and more importantly mobile networks will take to this. All still rumour at the moment.